1. Field of the Invention
This invention relates to a technique of driving a liquid crystal display, and more particularly to a method and apparatus for driving a liquid crystal display that is adaptive for eliminating a residual image generated upon the realization of a moving picture.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) of an active matrix driving system uses thin film transistors (TFTs) as switching devices and allows signals to be applied to each of the picture elements in the thin TFTs to thereby display a picture. For a given display screen size, an LCD device requires less space and consumes less power than a cathode ray tube (CRT) device. Accordingly, LCDs have been widely used as monitors for personal computers, notebook computers as well as office automation equipment such as copy machines, and a portable equipment such as cellular phones and pagers.
The active matrix LCD displays a picture corresponding to video signals, such as television signals, on a pixel (or picture element) matrix having liquid crystal pixel cells arranged between intersections between gate lines and data lines. The TFTs are arranged adjecently to each intersection between the gate lines and the data lines and are turned on when a scanning signal (i.e., a gate pulse) is applied from the gate line. Then, a data signal on the data line is transmitted to the liquid crystal cell.
As shown in FIG. 1, the conventional active matrix display includes a liquid crystal display panel 2 having liquid crystal pixel cells arranged in a matrix between two transparent substrates, a gate driver 6 connected to gate lines GL1 to GLm of the liquid crystal display panel 2, and a data driver 4 connected to data lines DL1 to DLn of the liquid crystal display panel 2. TFTs are arranged at intersections between the gate lines GL1 to GLm and the data lines DL1 to DLn, respectively. The gate driver 6 sequentially applies a gate pulse to the gate lines GL1 to GLm as a scanning signal to drive the TFT connected to the corresponding gate line. One period of the gate pulse GP applied to the gate lines GL1 to GLm is set to one frame interval (e.g., 16.67 ms in the case of a NTSC system). A semiconductor channel is formed between the source and the drain of a TFT by this gate pulse GP, thereby driving the TFT. At this time, the data driver 4 applies a video data signal Vdata as shown in FIG. 2 to the data lines DL1 to DLn. Thus, as shown in FIG. 3, the liquid crystal pixel cells are charged by the video data signal Vdata when the gate pulse GP is applied to the TFT, and maintains the video data signal Vdata during one frame after the gate pulse GP transitions (e.g., turns off) . When the TFT is driven again by applying the gate pulse GP in the next frame, the liquid crystal display pixel cell charges the video data signal Vdata to have a polarity contrary to that of the video data signal Vdata of the previous frame. Also, the liquid crystal display pixel cell maintains the charged video data signal Vdata during one frame after the gate pulse GP transitions (e.g., turns-off) . Thereafter, the liquid crystal pixel cells perform the above described steps repeatedly and the video data signal Vdata is charged with its polarity being inverted at each frame. The liquid crystal pixel cells have a rising transmissivity T during one frame charging of the video data signal Vdata in a normally black mode as shown in FIG. 4 to transmit light inputted from a backlight unit to a display screen.
Due to the time period when the liquid crystal pixel cells keep the video data during one frame and discharge the video data in a next frame, a residual image is left on the screen. Particularly, such a residual image causes a blurring phenomenon, a smearing phenomenon or a ghost phenomenon on the screen upon realization of a moving picture.
Recently, studies regarding a ferro-electric liquid crystal (FLC) and an anti-ferro-electric liquid crystal (AFLC) having a faster response speed than that of the conventional twisted nematic liquid crystal (TNLC) have been made. However, the LCD employing the FLC or AFLC has a problem in that, since it has a sufficiently rapid response speed of less than hundreds of microseconds, it is of great advantage to the realization of moving pictures, but it fails to completely eliminate a residual images when the LCD is driven by the conventional driving method.